Anti-lock brake device for use with a brake rotor disc

ABSTRACT

A disc brake assembly includes a rotor with an ABS tone ring insert assembly that functions as a rotation indicator in an anti-lock braking system. The insert is positioned in the hat of a rotor disc in a spaced relationship and is mounted to the mounting flange of the rotor disc. Forming the ring insert separately from the rotor disc also allows different coating materials to be used on the tone ring that may be more heat resistant. The ring insert assembly can be made of powder metal or made as a cast iron cylinder with a toothed cap made of powder metal having a corrosion resistant coating. Cost savings can be realized along with high performance when only a portion of the assembly if made of powder metal and coated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to brake assemblies, especially vehicular brakesincluding brake rotors attached to wheel hubs. This inventionparticularly relates to brake rotor disc assemblies equipped withanti-lock brake devices.

2. Description of Related Art

Typically, vehicles are equipped with a brake system to providecontrolled slowing or stopping of the wheels to halt movement of thevehicle. A common type of brake system is a disc brake assemblyassociated with the wheels that is actuated by hydraulic or pneumaticpressure generated by an operator of the vehicle depressing a footpedal. As is known, a disc brake assembly generally includes a rotorsecured to the wheel of the vehicle for rotation therewith. The rotorhas a pair of opposed friction plates that are selectively engaged bybrake shoes supported on opposite sides of the rotor for slidingmovement relative thereto.

In operation, the brake pads, which are operatively connected tohydraulically actuated pistons, move between a non-braking position inwhich they are spaced apart from the opposed friction plates of therotor and a braking position in which they are moved into frictionalengagement with the opposed friction plates of the rotor. In response toactuation by an operator, typically by depressing a brake pedal, thepiston urges the brake pads from the non-braking position to the brakingposition. By this, the brake pads frictionally engage the frictionplates of the rotor and slow or stop the rotation of the associatedwheel of the vehicle.

To improve braking control and vehicle safety, anti-lock brake systemshave been developed. In accordance with these systems, rotation of thewheel is sensed, and the braking response is automatically controlled toavoid skidding situations in which the vehicle wheels lose traction andslide over the pavement rather than engaging the surface at a slowerrotational speed.

In a typical anti-lock brake assembly 200 seen in FIGS. 8-11, the rotor210 is provided with a ring of teeth 212, which are cast with the rotor,commonly referred to as an ABS (Anti-lock Braking System) tone ring. Asthe rotor 210 rotates, the rotating teeth 212 are read by an anti-lockbrake sensor (not shown) that generates a signal for the anti-lock brakecontrol system representative of the rotation of the wheel associatedwith the rotor 210. The sensor reads the peaks of the teeth and thevalleys between adjacent teeth, best seen in FIGS. 10 and 11, and usesan algorithm to determine whether the associated wheel is slipping. Ifit is determined that the wheel is slipping, braking pressure isreleased. Obviously, the arrangement and geometry of the teeth influencethe signal generated by the sensor. To ensure proper operation of theanti-lock brake system, the teeth must be regularly spaced, sized, andmaintained to preserve the profile of the teeth. Many sensors usemagnetic pulse generation, which is created as the teeth pass by thesensor. The strength and accuracy of the signal is determined by themagnetic properties of the tone ring and the ring's geometric accuracy.Inadequate magnetic signal strength or incorrect geometric shape maycause signal failure, which can be further influenced by rotatingvelocity.

Problems have arisen with anti-lock brake systems in terms of poorperformance due to irregularities and corrosion of the teeth. In knownrotor assemblies in which the teeth are cast with the rotor, the teethare also subjected to machining and coating treatments that are appliedto the rotor. The disc is typically coated with an anticorrosivematerial, such as Geomet or Magni type coatings, that has a frictionproperty and a corrosion resistance property. The coating is intended tolengthen the shelf life of the rotor and impede corrosion. However,since the coating is present when the rotor is put in use and then wearsaway from the braking surface, the coating must have adequate frictionproperties so that the rotor functions properly during braking at theoutset before the coating is worn off. These dual property constraintslimit the possible types of coatings suitable for this application.

Another consideration regarding the coating relates to the teeth. Asnoted above, the teeth are cast with the rotor, and the coating isapplied to the entire piece. However, the teeth involve different designconsiderations. As the teeth do not function as a friction surface, thefriction property of the coating is irrelevant. Further, it is desirableto maintain the anti-corrosive coating on the teeth for the functionallife of the assembly. However, coatings suitable for rotor applicationdegrade at high temperatures. This does not pose a problem with respectto the braking surface, but the teeth are exposed to high temperaturesduring the braking process. Since they are formed integrally with therotor, which is normally cast iron, they heat to high temperatures, suchas 800-900° F., as the rotor heats up due to the heat generated duringbraking. When the coating breaks down, the teeth can corrode. Corrosionalters the geometry of the teeth and causes inaccurate readings from theanti-lock braking sensor. This significantly shortens the useful life ofthe brake rotor assembly. When the sensor generates inaccurate readings,the assembly requires repair or replacement.

A problem also exists due to the state of the art casting methods andtolerances, which exist in casting of the teeth. Cast teeth will not besufficiently accurate for most applications, and the inaccuracy ingeometry will cause signal failure at higher velocities. To furthermachine the teeth for accuracy adds significant additional cost.

Another problem with cast iron tone rings relates to the magneticproperties of cast iron and how the properties change with temperature.Since cast iron has a high carbon content, its magnetism is reduced whenheated to high temperatures experienced during braking.

There is a need, therefore, to provide a brake rotor assembly for usewith anti-lock brake systems that provides an accurate and durablesensor system. There is also a need for a sensor system that can beretrofit in existing assemblies that no longer provide accuratereadings.

SUMMARY OF THE INVENTION

An aspect of the invention provides a brake assembly having a rotor withan ABS tone ring for use with an anti-lock brake assembly that providesaccurate and reliable readings.

Another aspect of the invention provides a brake assembly having a rotorwith an ABS tone ring for use with an anti-lock brake assembly that hasa relatively long service life.

An additional aspect of the invention provides a brake assembly having arotor with an ABS tone ring for use with an anti-lock brake assemblythat accommodates more versatile and durable coatings suitable for hightemperature environments at a reasonable cost.

A further aspect of embodiments of the invention provides a tone ringassembly that can be retrofit in existing brake rotor systems.

The invention is directed to a brake rotor disc assembly comprising arotor disc having a braking surface and a hat portion for mounting to awheel hub, wherein the hat portion includes a cylindrical body and aradial mounting flange, and a tone ring insert for use with an anti-lockbraking system. The tone ring insert includes a cylindrical portion anda sensor flange having a radial surface with a plurality of spacedsensing formations disposed thereon. The cylindrical portion is mountedto the radial mounting flange such that the tone ring insert ispositioned within and spaced from the cylindrical body.

The invention is also directed to a brake rotor disc assembly comprisinga rotor disc, which has a braking surface and a hat portion for mountingto a wheel hub, and a tone ring insert assembly. The hat portionincludes a cylindrical body and a mounting flange. The tone ring insertassembly is designed for use with an anti-lock braking system andincludes a cylindrical spacer positioned in the hat portion and mountedto the mounting flange and a cap coupled to the cylindrical spacer andhaving a toothed flange.

The invention includes the brake rotor disc assembly in combination withan anti-lock braking system including a sensor that generates signalsbased on rotation of the tone ring insert assembly and in combinationwith a vehicle.

The invention further relates to a tone ring assembly for use in ananti-lock braking system comprising a cylindrical spacer having a firstend and a second end, wherein the first end has a plurality of axialopenings formed therein, and a cap having an axial engaging portion anda radial flange extending from the axial engaging portion, wherein theradial flange has a ring of spaced teeth formed in a surface thereof.The axial engaging portion is fixed to the second end of the cylindricalspacer.

In the tone ring assembly, the cylindrical spacer can be made of castiron, while the cap is made of powder metal in a high precision processand has a corrosion resistant coating thereon.

These and other aspects of the invention will become apparent in view ofthe detailed description and drawings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in conjunction with the following drawings inwhich like reference numerals designate like elements and wherein:

FIG. 1 is a top perspective view of the rotor disc assembly inaccordance with this invention;

FIG. 2 is a bottom view of the rotor disc assembly of FIG. 1;

FIG. 3 is a top view of the rotor disc assembly of FIG. 1;

FIG. 4 is a side view of rotor disc assembly of FIG. 1;

FIG. 5 is an exploded side view in partial section taken along line A-Aof FIG. 3;

FIG. 6 is an enlarged partial side view of in section taken along lineA-A of FIG. 3;

FIG. 7 is an exploded bottom perspective view of the assembly of FIG. 1;

FIG. 8 is a bottom perspective view of a prior art rotor disc assembly;

FIG. 9 is a bottom view of the rotor disc assembly of FIG. 8;

FIG. 10 is a sectional side view taken along line B-B of FIG. 9; and

FIG. 11 is an enlarged view of section C of FIG. 9.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The disc brake rotor assembly described herein is preferred for use onvehicles, including automobiles, racing vehicles, trucks, heavy dutytrucks, motorcycles and the like. The vehicles particularly suitable foruse with this invention can include those vehicles having a grossvehicle weight of about 10,000 pounds and above, especially deliverytrucks and buses. However, the inventive concepts discussed herein canbe used in any type of application that uses rotary brakes, includingautomotive, other types of motorized vehicles, or railcars. Theinvention is especially applicable for retrofitting in existingvehicles.

FIG. 1 shows a brake rotor disc assembly 10 in accordance with theinvention. The brake rotor disc assembly 10 includes a rotor disc 12having a pair of opposed braking plates 14, 16 with friction material onthe surface of each plate and a hat portion 18 for connection to a wheelhub (not shown) as is known. The hat portion 18 is defined by acylindrical body 19 and a mounting flange 20. The mounting flange 20 hasa series of openings 21 to receive fasteners for connection to the wheelhub. Another series of openings 22, best seen in FIG. 3, are provided onthe outer edge of the mounting flange 20. Preferably, the openings 22are formed as counterbores. The rotor disc 12 shown in FIG. 1 is aventilated disc with vanes 24 formed between the braking plates 14, 16;however, this invention can be employed in single plate discs as well,as would be readily recognized by those of ordinary skill in the art.The rotor disc 12 is preferably made of cast iron. However, anyconventionally known material may be used, including a composite.

In accordance with this invention, an independent toothed ring insertassembly or ABS tone ring insert is coupled to the rotor disc 12. Thetoothed ring insert can be formed as a single piece in which the ringhas teeth formed on a radial flange. With a single piece, any suitablematerial could be used. For example, the insert could be made entirelyof powder metal with a corrosion resistant coating formed thereon.Alternatively, the insert could be made by molding a steel stamping intoa high temperature resistant plastic or rubber. To reduce costs andoffer additional material alternatives, the insert could be formed intwo pieces. This configuration is illustrated in the drawings, but itwill be recognized to those of ordinary skill in the art that the designof a one-piece insert would be similar except that the two pieces wouldbe a unitary piece.

Referring to FIGS. 1-7, a toothed ring insert 26 is shown coupled to therotor disc 12. The insert 26 is formed in two pieces. The first piece isa cylindrical portion or spacer 28 having an annular side wall with aseries of axial counterbore threaded openings 30 formed in one end. Theother end has an interior annular groove 32 formed therein. Preferablythe cylindrical spacer 28 is formed of cast iron, which is durable andrelatively low cost. The second piece is a cap 34 that is formed as atoothed ring. The cap 34 is formed as a radial flange 36 including aring of spaced teeth 38 and an axial engaging portion 40. The cap 34 ismade with highly accurate geometry to form well defined teeth thatinteract with the ABS sensor. The teeth 38 can be any type of sensingformations, such as serrations, alternating peaks and valleys, oropenings. Preferably, the cap 34 is made by stamping, molding withpowder metal or by machining. For cost purposes, a powder metal part orstamped part is preferred.

This assembly takes advantage of the lower cost of the cast ironcylindrical spacer 28 and high geometric accuracy and heat resistantmagnetic properties of the powder metal cap 34 by connecting the twopieces together to act as the tone ring insert assembly 26. The couplingcan be achieved by a press fit, bolt, screw, pin, snap ring, thread ortongue and groove. One method of connection would be to use a protrudinglip on the cap that is press fit within the spacer 28 to engage theannular groove 32. Alternatively, the annular groove in the spacer 28could be formed as an exterior annular groove with the same connectingeffect. As best seen in FIGS. 5 and 6, a preferred method of connectionis to knurl or serrate the axial engaging portion 40 and press fit theportion 40 into the groove 32 of the spacer 28. Of course, any type ofknown connecting method can be used to achieve an integral componentformed of two separate pieces. For example, connection can be made by abolt, a pin, a snap ring, threads, or tongue and groove.

Another advantage of using two pieces for the tone ring insert 26 isthat only the cap 34 needs corrosion resistant coating to protect thegeometry of the teeth 38 and prevent corrosion build up to ensureaccurate readings from the ring. This reduces costs as the cast ironspacer 28 does not need a coating. A preferred coating is an electrolessplating process, as is known in the art. For example, electroless nickelcan be used for corrosion resistance. Of course, any suitable coatingcan be used, including any electro-plating, electroless-plating ormetallurgical plating. In the case of a one piece insert, the entirepiece could be coated if desired.

The ring insert 26 is assembled with the rotor disc 12 by inserting thering insert 26 into the hat portion 18, as seen in FIGS. 6-7. Aplurality of fasteners is used to connect the ring insert 26 to themounting flange 20 by extending through openings 22 into threadedopenings 30. By this, the ring insert 26 is fastened to the rotor disc12 at the wheel mounting face, which is the farthest point from the heatgenerating friction faces 14, 16 and is least susceptible to thermaldeformation. As seen in FIG. 6, the ring insert 26 is independent of andspaced from the cylindrical body 19, which provides some thermalinsulation to the ring insert 26, especially as compared to conventionalintegral toothed rotors in anti-lock brake assemblies. Also, since thering insert 26 is fastened to the mounting flange 20 and sits within thehat portion 18, radially inwardly from the braking plates 14, 16, anytwisting or bending experienced by braking plates 14, 16 due to thermalstresses induced during braking would not be translated to the ringinsert 26. Additionally, by forming the ring insert 26 separately fromthe rotor disc 12, the choice of coating materials for the cap 34 isexpanded as the coating material for the teeth does not need thefriction quality required by the braking plates 14, 16.

The assembly 10 can be originally manufactured or retrofit on vehiclesinto existing brake rotor systems to replace ABS systems that no longerprovide accurate readings due to incorrect geometries and/or corrosion.First, the cap 34 is fixed to the spacer 28 to assemble the tone ringinsert assembly 26. The assembly 26 is then secured to the mountingflange 20 of a brake rotor disc 12 with the fasteners as describedabove. The entire assembly 10 is then installed in place of aconventional brake rotor. Of course, if a one-piece insert is used, theentire insert is simply installed to the mounting flange of the brakerotor disc. Since the toothed cap 34 is formed with a high precisionprocess such as stamping, molded from powder metal, or machined, thegeometry is highly accurate. The corrosion resistant coating on thetoothed cap 34 ensures that corrosion will not occur and compromise thegeometry of the teeth or interfere with sensor readings. Accordingly, ahighly reliable brake rotor disc assembly 10 can be retrofit into anexisting vehicle at a relatively low cost.

It can be appreciated that the ring insert 26 functions in the samemanner as known toothed rings associated with brake rotor discs withanti-locking braking systems. The rotation of the teeth 38 is sensed byan anti-locking sensor to assess whether the wheel is slipping. Thebraking action is adjusting accordingly. Using this invention, however,will provide a more accurate and reliable reading since corrosion of theteeth is minimized and the teeth can be formed with high precision. Thisinvention will also provide a longer service life for brake assemblies,especially in large vehicles, such as delivery trucks and buses andallow degraded tone rings to be easily replaced.

The invention is not limited to those embodiments described herein andmay encompass various changes and modifications. It will be understoodthat the various modifications shown herein can be used in anycombination. It is also possible to eliminate various components of theassembly and still have an effective connection. Further, differentmaterials may be used to obtain similar results.

1. A brake rotor disc assembly comprising: a rotor disc having a brakingsurface and a hat portion for mounting to a wheel hub, wherein the hatportion includes a cylindrical body and a radial mounting flange; and atone ring insert for use with an anti-lock braking system including acylindrical portion having an outer cylindrical surface and a sensorflange having a radial surface with a plurality of spaced sensingformations disposed thereon, wherein the cylindrical portion is mountedto the radial mounting flange such that the entire outer cylindricalsurface of the cylindrical portion is positioned within and spaced fromthe cylindrical body, so as to thermally insulate the tone ring insertwherein the cylindrical portion of the tone ring insert has threadedaxial bores therein for receiving a fastener for coupling to the rotordisc.
 2. The assembly of claim 1, wherein the tone ring insert is formedas a unitary ring.
 3. The assembly of claim 1, wherein the tone ringinsert is formed in two pieces, with the cylindrical portion connectedto the sensor flange.
 4. The assembly of claim 3, wherein thecylindrical portion and the sensor flange are formed of differentmaterials.
 5. The assembly of claim 4, wherein the cylindrical portionis formed of cast iron and the sensor flange is formed of powder metal.6. The assembly of claim 3, wherein the sensor flange is press fit intothe cylindrical portion.
 7. The assembly of claim 3, wherein thecylindrical portion has an annular groove on one end and the sensorflange has an axial engaging portion that is received in the annulargroove.
 8. The assembly of claim 1, further comprising a plurality ofbolts extending through the mounting flange and threadably engaged withthe tone ring insert.
 9. The assembly of claim 1, wherein the tone ringinsert has a non-corrosive coating thereon.
 10. The assembly of claim 9,wherein the tone ring insert is plated with electroless plating.
 11. Theassembly of claim 1, in combination with an anti-lock braking systemincluding a sensor that generates signals based on rotation of the tonering insert.
 12. The assembly of claim 1, in combination with a vehicle.13. The assembly of claim 1, in combination with a vehicle having agross vehicle weight of at least 5,000 pounds.
 14. A brake rotor discassembly comprising: a rotor disc having a braking surface and a hatportion for mounting to a wheel hub, wherein the hat portion includes acylindrical body and a mounting flange; and a tone ring insert assemblyspaced from said cylindrical body so as to thermally insulate said tonering insert assembly for use with an anti-lock braking system includinga cylindrical spacer having an outer cylindrical surface positionedconcentrically in the hat portion and a cap coupled to the cylindricalspacer having a toothed flange, wherein the entire outer cylindricalsurface is spaced from said cylindrical body wherein the cylindricalspacer of the tone ring insert assembly has threaded axial borestherein.
 15. The assembly of claim 14, wherein the cylindrical spacerand the cap of the tone ring insert assembly are formed of differentmaterials.
 16. The assembly of claim 14, wherein the cylindrical spacerof the tone ring insert assembly is formed of cast iron.
 17. Theassembly of claim 14, wherein the cap of the tone ring insert assemblyis formed of powder metal.
 18. The assembly of claim 14, wherein the capof the tone ring insert assembly is formed by stamping.
 19. The assemblyof claim 14, wherein the cap of the tone ring insert assembly is formedby machining.
 20. The assembly of claim 14, wherein the cap is press fitinto the cylindrical spacer.
 21. The assembly of claim 14, wherein thetone ring insert assembly is connected to the hat portion at a positionfarthest from the braking surface of the rotor disc.
 22. The assembly ofclaim 14, wherein the cylindrical spacer of the tone ring insertassembly is fastened to the mounting flange of the rotor disc.
 23. Theassembly of claim 14, wherein the cylindrical spacer has an annulargroove on an end opposed to the axial bores and the cap has an axialengaging portion that is received in the annular groove.
 24. Theassembly of claim 14, further comprising a plurality of bolts extendingthrough the mounting flange and threadably engaged with the cylindricalspacer of the tone ring insert assembly.
 25. The assembly of claim 14,wherein the cap has a non-corrosive coating thereon.
 26. The assembly ofclaim 25, wherein the cap is plated with electroless plating.
 27. Theassembly of claim 14, wherein the toothed flange is substantiallyparallel to the braking surface of the rotor disc.
 28. The assembly ofclaim 14, in combination with an anti-lock braking system including asensor that generates signals based on rotation of the tone ring insertassembly.
 29. The assembly of claim 14, in combination with a vehicle.30. The assembly of claim 14, in combination with a vehicle having agross vehicle weight of at least 5,000 pounds.
 31. A tone ring assembly,comprising: a cylindrical spacer having a single outer diameter definingan outer cylindrical surface, a first end and a second end, said outerdiameter sized to enable said cylindrical spacer to be positionedconcentrically within a hat portion of a rotor disc, so that said outercylindrical surface is spaced apart from the hat portion, so as tothermally insulate said tone ring insert, wherein the first end has aplurality of axial openings formed therein; and a cap having an axialengaging portion and a radial flange extending outward from the axialengaging portion, wherein the radial flange has a ring of spaced teethformed in a surface thereof, wherein the axial engaging portion is fixedto the second end of the cylindrical spacer.
 32. The assembly of claim31, wherein the axial engaging portion is press fit within the secondend of the cylindrical spacer.
 33. The assembly of claim 31, wherein anannular groove is formed in the second end of the cylindrical spacer andthe axial engaging portion is knurled.
 34. The assembly of claim 31,wherein the cylindrical spacer is made of cast iron.
 35. The assembly ofclaim 31, wherein the cap is formed of powder metal.
 36. The assembly ofclaim 31, wherein the cap is formed by machining, stamping or molding.37. The assembly of claim 31, wherein the cap has a corrosion resistantcoating formed thereon.
 38. The assembly of claim 31, wherein the cap iselectroless plated.
 39. The assembly of claim 31, in combination with abrake rotor.
 40. The assembly of claim 39, further comprising fastenersthat extend into the axial openings in the cylindrical spacer to connectthe assembly to a mounting flange of a brake rotor.
 41. The assembly ofclaim 39, wherein the brake rotor includes a braking disc mounted on oneend of a cylindrical body and a mounting flange mounted on the other endof the cylindrical body, wherein the fasteners extend through themounting flange to connect to the assembly.
 42. The assembly of claim31, in combination with a brake rotor, wherein the assembly is retrofitin an anti-lock braking system.
 43. The assembly of claim 31, incombination with a vehicle.
 44. The assembly of claim 31, in combinationwith a vehicle having a gross vehicle weight of at least 5,000 pounds.